Ordinarily thermocouples are formed of two dissimilar materials joined at a junction with the open legs of the thermocouple connected to an electrical loan and at a lower temperature than the junction where the two dissimilar materials are joined. The temperature differential produces a flow of electrons and this flow can be measured. Common use of the thermocouple is to measure temperature.
Thermopiles are usually made of thermocouples connected in series with the strings of series connected thermocouples connected in parallel in order to maximize current and voltage output.
When thermocouple conductor elements are connected together in series to form a thermopile, one group of junctions will be in a cold zone where heat is removed, and the other group of junctions will be in a heated area. The electrons which carry the current and the heat energy, surrender the heat at the lower temperature junction. The Peltier effect is produced at each junction but in the opposite direction at each. Because there is a temperature difference between the reservoirs in contact with the legs of the thermocouples, the temperature gradient is produced along their length. This temperature gradient also leads to the production of an electric current and this process is called the Thomson effect.
In practice, hundreds or thousands of thermocouples can be connected in series to produce sizable voltages.
Additional banks of thermocouples can then be connected in parallel with the net result that a source of a significant amount of current at high voltage is developed. This technique has been used to generate electricity in extremely small quantities.
Likewise, utilizing the reverse effect by introducing electricity into this system, and having the hot junction in the ambient air and the cold junction in a contained zone to be cooled, the Peltier effect can be utilized to produce refrigerating device, again of low efficiency, however.
Recently it has been recognized that if the cross-sectional area of the junction is larger than the cross-sectional area of the thermocouple legs, certain improvements in the efficiency of the device can be obtained. U.S. Pat. No. 4,251,290, Gomez, U.S. Pat. No. 4,251,291, Gomez, and U.S. Pat. No. 4,257,822, Gomez, all disclose this feature. This disclosure is based on the improvement in efficiencies based on the fact that there is a minimum of heat transfer across the junction since the legs of the thermopile are relatively thin in their cross-sectional area compared with the junction and thus heat flow is minimized and the temperature difference between the thermoelectric junctions is maximized and thus the voltage developed therebetween is increased. Unfortunately, there is no indication in the Gomez disclosures of the degree of improvement obtained.